OMFGWTFBBQ is an acronym for Oh My Fucking God What The Fuck Bar-B-Que.
This acronym arose from the need to find a way to lengthen an already retardedly long acronym ("OMFGWTF"). Perhaps an internet-user found himself so aghast and bewildered at an event, OMFGWTF was simply not sufficient to articulate it. No one knows why Bar-B-Que was chosen. Presumably because it was already a well known acronym, and had absolutley nothing to do with OMFGWTF.
A similar treatment of extending lengthy acronyms with nonsense can be seen with ROFLMAOSTC.